A New Year's Eve party planned for Sydney's Wet N Wild waterslide park has been cancelled at the last minute, throwing the plans of hundreds of revellers into chaos.

A music festival for over 16s was due to be held at the theme park, which opened at Prospect in Sydney's west earlier this month.

Acts billed to play included Gtronk from Belgium, F.O.O.L from Sweden and local star Faydee.

A spokesman for the park said tonight's function was not organised by the park.

In a statement, promoters One Cube Entertainment said the "very difficult decision" had been made to postpone the event to Australia Day.

"This decision is in the best interest of our patrons due to some last-minute production issues," the statement said.

"We sincerely apologise for any inconvenience caused and are currently working on something bigger and better for Australia Day."

The promoters say ticket holders can either go to Parramatta venue The Roxy tonight to watch the same line-up or go to the rescheduled event on January 26.

But many ticket holders are furious at the last-minute change, taking to the festival's Facebook page to vent their anger.

One woman Natasha Rogers wrote:

Wet n wild your (sic) going to get a flogging this week over the phone from myself and my fiancee as well as friends. We received the email that it was post phoned (sic) when we're driving down the freeway to your venue that's nearly 3 hours away. Not only have you wasted our fuel and money but u made us fork out money on dressy clothes for tonight just so we can get into a nightclub since we packed swimmers.

Another poster Michelle Warren wrote:

Wet n Wild this is absolutely disgusting, you should be refunding everyone who bought a ticket not make them hold out god (sic) another event which is also likely to be cancelled. You guys are the worst organised park ever to be opened. So wrong. You just keep making excuse after excuse. With broken down equipment to closing down the park what every day, WTF!!!!!!!!!!

Since its opening, Wet N Wild has regularly reached capacity and been forced to turn customers away, and several rides have been closed on different days.

New South Wales Fair Trading Minister Stuart Ayres said it was unacceptable for organisers to leave ticket holders for tonight "high and dry".

He says a case manager has been appointed to deal with complaints and that refunds should be provided to those who want them.

“We want to ensure consumers are dealt with according to Australian Consumer Law (ACL) provisions,” he said in a statement.

“These provisions require consumers to receive a full refund when services are not provided, if they so choose.

“We understand the promoters are planning to re-stage the event on Australia Day.

“We expect them to provide full refunds to patrons who want one."

The minister says the law provides for consumers to received compensation for consequential losses.